This application is a national phase of PCT/FR99/01319 which was filed on Jun. 4, 1999 and was not published in English.
The invention relates to the field of electrical sampling, particularly of pulses of short or very short duration.
The metrology of pulses enables one to describe the evolution in time of a signal, or an electrical pulse, in particular its voltage or its energy, when this signal, or this pulse, is, for example, unique (i.e. non-repetitive), and very brief (that is to say, has a duration of the order of a few tens or a few hundreds of picoseconds).
Such pulses to be measured generally arise from very fast radiation detectors, which convert into electrical pulses, the energy of a pulse of radiation that they receive, for example, a pulse of X, or gamma, or visible, or infra-red radiation. Such radiation can be emitted by ultra-fast radiation sources, such as lasers or sources of synchrotron radiation, or can be the result of a laser-material interaction caused by an ultra-fast laser (that is to say, the duration of the pulse is in the picosecond or femtosecond range).
The invention can be applied to any measurement of a very brief electrical signal, particularly a non-repetitive signal, in particular in the physics of events, or in the measurement of events, generated by picosecond phenomena.
There currently exist on the market sampling oscilloscopes for the measurement of signals whose spectrum extends to 50 GHz or 70 GHz. These pieces of equipment enable one to measure repetitive pulses. The sampling frequency is variable between from 250 kHz to 1 GHz.
In order to measure single pulses, commercial equipment exists on the market: this equipment enables one to reconstruct a spectrum up to 5 GHz or 7 GHz.
Among the laboratory prototypes, a known device is that described in document U.S. Pat. No. 5,471,162. Such a device rests on the principle of spatial sampling of a pulse. A pulse propagates along its line of propagation. The result is a spatial equivalent of the evolution, over time, of this pulse which is propagated on the line with a speed depending on its physical characteristics. At a specified instant t, if the line is of sufficient length, the whole of the pulse is distributed spatially along the line.
If the samplers are arranged along the line of propagation, their simultaneous actuation allows one to carry out complete sampling of the pulse, with a time step equal to the spatial step of the samplers, divided by the speed of propagation.
An optical sampling device is also known which measures signals with a bandwidth up to 35 GHz. This device is illustrated in FIG. 1. It comprises a line of propagation 2 into which a pulse signal 4 to be measured is inserted and along which it propagates. Along the line of propagation sampling ports 6, made of a photo-conductive material (CdTe), are arranged in a regular manner. These sampling ports are associated with sampling lines 8, each of which is connected to charge reading means. The set of charge reading means is gathered into a charge reading device 10. These charge reading means are connected to a computer 12 programmed to measure the relative charges on each channel and to analyze the pulse 4. Each sampling port 6 has its circuit closed by a triggering light pulse 14: a triggering light pulse is necessary which is distributed over all the sampling ports. Therefore, this device requires a picosecond optical flash of a few tens of nanojoules to trigger the sampling.
These known samplers are therefore photo-conductors, in the case of the optical sampler (FIG. 1) and diodes in the case of the compact digitizer.
In these known structures, samplers sample a part of the signal present at their position on the line. They are placed in parallel, on this line of propagation.
Document FR-97 06534 describes a single action electrical sampler for short pulses.
The principle of this electrical sampler, with line sections is illustrated in FIG. 2.
A structure, or line, 24 of propagation of electrical pulses comprises a plurality of sections 18, 20, 22 of this structure. The different sections are linked, two by two, through switches 28, 29, constituted by, for example, MESFET AsGa (or Si, or MOS transistors or bipolar transistors on Si).
The command means for the switches 28, 29 comprise, for example, a second structure 26 for the propagation of a triggering pulse, to which the switches 28 are connected.
In FIG. 2, only three sections of the line 24 have been shown, but the line may comprise any number of sections, separated, two by two, and connected two by two, by the switches.
A signal to be sampled propagates along the propagation structure, or the line of propagation 24.
Along the line of propagation 26, a synchronization signal is propagated, for example a voltage step slot. The switches are normally on, or closed, and the voltage step opens these switches. This step or slot, therefore isolates each section of the line of propagation, which is then used as a storage capacitance.
The whole of the charges transported by the pulse is then confined in the different sections 18, 20, 22 that make up the pulse propagation structure.
The structure illustrated in FIG. 2 thus comprises:
on the one hand, a first propagation structure 24 where the quantity of charges to be measured is propagated and which is made up of sections connected two by two by switches which are initially closed,
on the other hand, a second propagation structure in which a synchronization signal of the xe2x80x9cstepxe2x80x9d type can be propagated; at the moment the step passes, this modifies the command of the state of the switch in such a way that it opens and isolates the two sections to which it is connected, charges then being trapped in a section when the two switches which mark its limits are open. It is these charges which are subsequently read by a suitable reading device.
The device is completed by means of generating a synchronization signal, these means being connected to the structure 26 for propagating synchronization pulses. In addition, they can be connected to a device for reading the charges in the sections.
These samplers have a restricted bandwidth, linked to the bandwidth of the line itself. Furthermore the sensitivity of detection (that is to say the quantity of charges sampled in the signal) is also limited. With regard to the optical sampler, the use of a picosecond, high power laser imposes very great financial and experimental constraints.
Finally, all these devices require a very long propagation line, corrupting the signal in a non-uniform manner.
The invention relates to a novel electrical sampler. In particular, it relates to an analyzer of fugitive signals, that uses a non-simultaneous spatial sampling method.
It also relates to an analyzer of fugitive signals, that uses a new technology for coupling substrates.
Such an analyzer can be used for laser diagnostics. Its field of application also extends to the measurement of rapid single signals of any origin, through a simple adaptation.
More precisely, the subject of the invention is an electrical sampler, characterized in that it comprises:
a structure for the propagation of electrical pulses,
N means of sampling connected, on the one hand, to sampling points along the propagation structure, and, on the other hand, to means for the propagation of sampling signals,
means to temporally delay the propagation of a sampling signal between two consecutive sampling means.
A spatial sampling device according to the invention uses as many elementary samplers as there are samples to be taken. Each elementary sampler only functions once by acquisition. The signal is propagated on a propagation support matched to the frequencies to be analyzed, along which the samplers are arranged sequentially in such a way that the signal passes in front of each of them with a time shift that is linked to the spatial step of the layout of the samplers and to the temporal delay means of the sampling signal.
The acquisition or sampling signal is transmitted from sampler to sampler. The combination of the delay time between two samples and the propagation time of the signal on the line determines the sampling step of the device. Hence non-simultaneous spatial sampling is being carried out. This means that a very long propagation line which corrupts the signal in a non-uniform way is not necessary.
The length of this line is greater than or equal to the sum of the spaces taken up by the switches. One switch, together with its connections occupies, for example, a space of 50 xcexcm.
Therefore the invention enables a line that is smaller than those of the prior art to be used. The line can be smaller than the space occupied by the pulse to be measured.
Means may be provided, on the propagation line, for sampling orders, in order to vary the delay between two successive samplers.
According to this embodiment, it is therefore possible to vary the sampling time step, by varying the delay between two successive samplers. This delay can be chosen by the user according to the sampling frequency and the analysis window for which it is needed.
According to another aspect of the invention, an electrical sampler comprises a structure for propagation of electrical pulses, created on a first substrate. Voltage pulses are sampled on this propagation structure using sampling and tapping means created on a second substrate. In addition, these means are connected to means of storing or storing and reading the charges corresponding to the pulses sampled.